How to Calculate Your Exact Age
Understand how calendar age is calculated in years, months and days, including birthdays and leap years.
In this guide
Why subtracting the years is only an estimate
If someone was born in 1990 and the current year is 2026, saying they are 36 may be right or wrong depending on whether their birthday has happened yet. Exact age needs the actual dates, not just the years.
Years, months and days
A calendar-based calculation first works out complete years, then complete months, and finally the remaining days. This is why the result can say something like 35 years, 7 months and 12 days rather than giving a decimal age.
Birthdays and leap years
The length of a month is not fixed, and February can have 28 or 29 days. A proper calendar calculation therefore needs to work with real dates instead of assuming every month or year has the same number of days.
Choosing the comparison date
You can calculate age as of today or as of a particular date. A historical or future comparison date can be useful when checking eligibility, planning an event or preparing records.
Try the related tool
If you came here because you need to do the calculation or create something now, you can use the matching KingToolsKit tool and then come back to the guide when you want the explanation.
Open the tool →